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Apr 30, 2022
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Add support for unwinding during prologue/epilogue #7

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156 changes: 156 additions & 0 deletions libunwind/src/CompactUnwinder.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -310,6 +310,50 @@ int CompactUnwinder_x86_64<A>::stepWithCompactEncodingRBPFrame(
uint32_t savedRegistersLocations =
EXTRACT_BITS(compactEncoding, UNWIND_X86_64_RBP_FRAME_REGISTERS);

// If we have not stored EBP yet
if (functionStart == registers.getIP()) {
uint64_t rsp = registers.getSP();
// old esp is ebp less return address
registers.setSP(rsp+8);
// pop return address into eip
registers.setIP(addressSpace.get64(rsp));

return UNW_STEP_SUCCESS;
} else if (functionStart + 1 == registers.getIP()) {
uint64_t rsp = registers.getSP();
// old esp is ebp less return address
registers.setSP(rsp + 16);
// pop return address into eip
registers.setIP(addressSpace.get64(rsp + 8));

return UNW_STEP_SUCCESS;
}

// If we're about to return, we've already popped the base pointer
uint8_t b = addressSpace.get8(registers.getIP());

// This is a hack to detect VZEROUPPER but in between popq rbp and ret
// It's not pretty but it works
if (b == 0xC5) {
if ((b = addressSpace.get8(registers.getIP() + 1)) == 0xF8 &&
(b = addressSpace.get8(registers.getIP() + 2)) == 0x77)
b = addressSpace.get8(registers.getIP() + 3);
else
goto skip_ret;
}

if (b == 0xC3 || b == 0xCB || b == 0xC2 || b == 0xCA) {
uint64_t rbp = registers.getSP();
// old esp is ebp less return address
registers.setSP(rbp + 16);
// pop return address into eip
registers.setIP(addressSpace.get64(rbp + 8));

return UNW_STEP_SUCCESS;
}

skip_ret:

uint64_t savedRegisters = registers.getRBP() - 8 * savedRegistersOffset;
for (int i = 0; i < 5; ++i) {
switch (savedRegistersLocations & 0x7) {
Expand Down Expand Up @@ -430,6 +474,118 @@ int CompactUnwinder_x86_64<A>::stepWithCompactEncodingFrameless(
}
}
}

// Note that the order of these registers is so that
// registersSaved[0] is the one that will be pushed onto the stack last.
// Thus, if we want to walk this from the top, we need to go in reverse.
assert(regCount <= 6);

// check whether we are still in the prologue
uint64_t curAddr = functionStart;
if (regCount > 0) {
for (int8_t i = (int8_t)(regCount) - 1; i >= 0; --i) {
if (registers.getIP() == curAddr) {
// None of the registers have been modified yet, so we don't need to reload them
framelessUnwind(addressSpace, registers.getSP() + 8 * (regCount - (uint64_t)(i + 1)), registers);
return UNW_STEP_SUCCESS;
} else {
assert(curAddr < registers.getIP());
}


// pushq %rbp and pushq %rbx is 1 byte. Everything else 2
if ((UNWIND_X86_64_REG_RBP == registersSaved[i]) ||
(UNWIND_X86_64_REG_RBX == registersSaved[i]))
curAddr += 1;
else
curAddr += 2;
}
}
if (registers.getIP() == curAddr) {
// None of the registers have been modified yet, so we don't need to reload them
framelessUnwind(addressSpace, registers.getSP() + 8*regCount, registers);
return UNW_STEP_SUCCESS;
} else {
assert(curAddr < registers.getIP());
}


// And now for the epilogue
{
uint8_t i = 0;
uint64_t p = registers.getIP();
uint8_t b = 0;

while (true) {
b = addressSpace.get8(p++);
// This is a hack to detect VZEROUPPER but in between the popq's and ret
// It's not pretty but it works
if (b == 0xC5) {
if ((b = addressSpace.get8(p++)) == 0xF8 && (b = addressSpace.get8(p++)) == 0x77)
b = addressSpace.get8(p++);
else
break;
}
// popq %rbx popq %rbp
if (b == 0x5B || b == 0x5D) {
i++;
} else if (b == 0x41) {
b = addressSpace.get8(p++);
if (b == 0x5C || b == 0x5D || b == 0x5E || b == 0x5F)
i++;
else
break;
} else if (b == 0xC3 || b == 0xCB || b == 0xC2 || b == 0xCA) {
// i pop's haven't happened yet
uint64_t savedRegisters = registers.getSP() + 8 * i;
if (regCount > 0) {
for (int8_t j = (int8_t)(regCount) - 1; j >= (int8_t)(regCount) - i; --j) {
uint64_t addr = savedRegisters - 8 * (regCount - (uint64_t)(j));
switch (registersSaved[j]) {
case UNWIND_X86_64_REG_RBX:
registers.setRBX(addressSpace.get64(addr));
break;
case UNWIND_X86_64_REG_R12:
registers.setR12(addressSpace.get64(addr));
break;
case UNWIND_X86_64_REG_R13:
registers.setR13(addressSpace.get64(addr));
break;
case UNWIND_X86_64_REG_R14:
registers.setR14(addressSpace.get64(addr));
break;
case UNWIND_X86_64_REG_R15:
registers.setR15(addressSpace.get64(addr));
break;
case UNWIND_X86_64_REG_RBP:
registers.setRBP(addressSpace.get64(addr));
break;
default:
_LIBUNWIND_DEBUG_LOG("bad register for frameless, encoding=%08X for "
"function starting at 0x%llX",
encoding, functionStart);
_LIBUNWIND_ABORT("invalid compact unwind encoding");
}
}
}
framelessUnwind(addressSpace, savedRegisters, registers);
return UNW_STEP_SUCCESS;
} else {
break;
}
}
}

/*
0x10fe2733a: 5b popq %rbx
0x10fe2733b: 41 5c popq %r12
0x10fe2733d: 41 5d popq %r13
0x10fe2733f: 41 5e popq %r14
0x10fe27341: 41 5f popq %r15
0x10fe27343: 5d popq %rbp
*/


uint64_t savedRegisters = registers.getSP() + stackSize - 8 - 8 * regCount;
for (uint32_t i = 0; i < regCount; ++i) {
switch (registersSaved[i]) {
Expand Down